1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor, and more specifically to a coating liquid for an undercoat layer for forming an under coat layer to be disposed between an electrically conductive support and a photosensitive layer and a method for producing the same, and an electrophotographic photoreceptor and an image forming apparatus using the same.
2. Description of the Related Art
Generally, an electrophotographic process using a photoconductive photoreceptor is one of information recording means utilizing a photoconductive phenomenon of a photoreceptor.
In this process, first, surface of a photoreceptor is caused to be uniformly charged by corona discharge in a dark place, and then an image is exposed to light to cause selective discharge of electric charges in the exposed part, whereby an electrostatic image is formed in the part not exposed to light. Then, colored charged microparticles (toner) are adhered to the latent image via electrostatic attractive force or the like to make a visible image, and thus an image is formed.
In the series of processes as described above, for example, the following fundamental characteristics are requested for a photoreceptor.
1) capable of being uniformly charged at an appropriate potential in a dark place;
2) having a high charge retaining ability with little discharging of electric charges in a dark place;
3) having excellent photo sensitivity, and rapidly discharging electric charges in response to light exposure.
It is also requested to be able to readily removing charges on a surface of a photoreceptor, to have small residual potential, to have mechanical strength, excellent flexibility, to cause no variations in electric characteristics, in particular, chargeability, photo sensitivity, residual potential in the case of repeated use, and to have characteristics of great stability and durability, for example, having resistance to heat, light, temperature, humidity, ozone deterioration and the like.
An electrophotographic photoreceptor that is put into practical use at present is constructed by forming a photosensitive layer on an electrically conductive support, however, since carrier injection is likely to occur from the electrically conductive support, an image defect occurs due to microscopic disappearance or reduction of surface electric charges.
In order to prevent such an image defect, and to achieve coverage of the defect on a surface of the electrically conductive support, improvement of chargeability, improvement of adhesion of the photosensitive layer, improvement of coating performance and the like, a measure has been taken to provide an undercoat layer between the electrically conductive support and the photosensitive layer.
Conventionally, as an undercoat layer, those comprising various resin materials, inorganic compound particles, for example, titanium oxide powder and so on are considered.
As a material that is used when an undercoat layer is formed by a resin single layer, examples including resin materials such as polyethylene, polypropylene, polystyrene, an acrylic resin, a vinyl chloride resin, a vinyl acetate resin, a polyurethane resin, an epoxy resin, a polyester resin, a melamine resin, a silicon resin, a polyvinyl butyral resin, a polyamide resin and the like, and copolymer resins including two or more of these repeating units, and additionally, casein, gelatin, polyvinyl alcohol, ethyl cellulose and the like are known, and among these, particularly preferred is a polyamide resin (Japanese Patent Application Laid-Open Publication No. 48-47344).
However, in an electrophotographic photoreceptor in which a resin single layer of polyamide or the like is used as an undercoat layer, accumulation of residual potential is large, so that reduction in sensitivity and fogging in an image occur. This tendency is significant, in particular, in an environment of low humidity.
In view of the above, for a purpose of preventing occurrence of image defect due to influence of the electrically conductive support, or improving the residual potential, those comprising titanium oxide powder having an untreated surface in an undercoat layer (Japanese Patent Application Laid-Open Publication No. 56-52757), those comprising titanium oxide microparticles covered with alumina for improving the dispersibility of titanium oxide powder (Japanese Patent Application Laid-Open Publication No. 59-93453), those comprising metal oxide particles having subjected to a surface treatment with a titanate-based coupling agent (Japanese Patent Application Laid-Open Publication No. 4-172362) and the like have been proposed.
However, proposals in these publications are still insufficient in terms of characteristics, so that there is still a need of an electrophotographic photoreceptor having more excellent characteristics.
It is an object of the present invention to provide a coating liquid for an undercoat layer of an electrophotographic photoreceptor having excellent dispersibility and temporal stability, and excellent coating performance to an electrically conductive support and capable of forming a uniform undercoat layer, and a method for producing the same, and to provide an electrophotographic photoreceptor suffering little change in electric characteristics and having good image characteristics after repeated use, using the coating liquid for an undercoat layer of an electrophotographic photoreceptor, and an image forming apparatus using the electrophotographic photoreceptor.